The present invention relates to protective apparatus for a computer and other types of sensitive electrical or electronic loads, and more particularly to apparatus for insertion in a computer power cable to protect the associated computer from power transients, excessive ambient temperatures, and emergency conditions. Furthermore, the present invention relates to manually resettable computer protective apparatus.
A number of voltage/current sensitive control circuits, temperature-sensitive switch circuits, and transient suppression circuits are found in the prior art. Generally they are intended for specific applications.
In the category of voltage/current sensitive supply switching circuits, U.S. Pat. No. 3,037,151, issued to Cimerman et al on May 29, 1962, discloses a voltage monitoring circuit for interrupting the power being supplied to a plurality of power supplies when the ratio of the output voltages from those power supplies sufficiently varies from a predetermined value. An actuating coil of a normally-closed relay switch opens that switch to interrupt the power. U.S. Pat. No. 3,167,685, issued to Bade et al on Jan. 26, 1965, discloses a computer protection circuit that monitors the output of a plurality of power supplies and, in the event of a failure of any one or more of the power supplies quickly removes all power being supplied from them to the computer. Each power supply includes an overload relay. In the event of a power supply failure, the computer protection circuit short-circuits the outputs of the power supplies, thereby overloading the power supplies. The overload relay of each power supply responds by opening the associated power supply line, which remains open until the relay is reset.
In the category of temperature sensitive switch circuitry, U.S. Pat. No. 2,597,185, issued to Roeding et al on May 20, 1952, discloses a self-protected distribution transformer having two bimetal elements responsive both to the temperature of the transformer oil and to the current flowing in the transformer secondary circuit. Either bimetal element is effective to trip a breaker, thereby interrupting the current flow through both poles of the breaker and completely disconnecting the secondary circuit from the distribution circuit supplied from the transformer.
In the category of transient protection circuitry, U.S. Pat. No. 4,023,071, issued to Fussell on May 10, 1977, U.S. Pat. No. 4,068,279, issued to Byrnes on Jan. 10, 1978, and U.S. Pat. No. 4,152,743, issued to Comstock on May 1, 1979 disclose varistors in suitable circuits for providing transient voltage protection. The patent to Comstock further discloses certain temperature sensitive devices in series with a respective varistor. These devices conduct when the current therethrough or the temperature thereof is below a certain level, and do not conduct when the current therethrough or the temperature thereof exceeds a certain level.
Therefore, it is desirable to provide a simply installed apparatus for protecting a computer system from harmful power line voltage transients, and for cutting off power to the computer in the event of excessive computer room ambient temperature and other such environmental conditions, source power failure, and emergency conditions. It is desirable for power cut-off due to such conditions as excessive temperature and source power failure to be automatic. Emergency conditions, which require operator discretion, should not cause automatic power cut-off; rather, the capability for manual cut-off is desirable therefor. Furthermore, restoration of power to the computer should not occur with power failure recovery or correction of the condition. Restoration of power requires the discretion of the computer operator, and therefore should be manually effected. It is desirable for the protective apparatus to be compatible with a wide variety of computer systems, particularly those powered by conventional one or three phase A.C. supplies.